Children acquiring a language are faced with at least two lexical tasks: learning new words and organizing these to uniquely distinguish each word from every other. During this process, children are also learning the phonological system, and it is likely that advances in lexical and phonological development influence one another. The long-term goal is to establish how clinical populations of children build a lexicon, how this interfaces with the phonological system, and how treatment programs may efficaciously remediate potential deficits in this area. To achieve this, our immediate goal is to determine how preschool children with age- appropriate language development build a lexicon because it is essential to document the normal process in order for disordered processes to be understood. Toward this end, mentored training and research programs are proposed. The training program focuses on the PI's development of appropriate research skills in longitudinal data analysis, single-subject research design, cognitive modeling, and clinically applied research particularly in terms of specific language impairment and functional phonological disorders. The complementary research program proposes two projects to (1) explore the processes underlying learning of the phonological forms of new words and examine the structure of word representations in preschool children, and (2) investigate the influence of phonological development on word learning and representations. The findings to emerge hold potential for theories of word learning and the relationship between perception and production in language acquisition.